1. Field of the Invention
The invention relates to an electrode coated with a new electroactive polymer obtained by electrochemical oxidization of a monomer and application thereof to electrochemical cells and more especially to electrochemical display systems.
2. Description of the Prior Art
Electrodes coated with a polymer film have already been produced, more especially for manufacturing electrochemical cells. Organic polymer eletrochromes are of great interest because they are easier to use than other types of electrochromes. Furthermore, by modifying the chemical structure of the polymer, the absorption spectra of the oxidized and reduced molecules may be modified. Electrochrome polymers in which the electrochrome group has been fixed by a chemical reaction to the chain of a polymer have already been described. Polymers soluble in organic solvents may be readily deposited on an electrode by conventional methods (by centrifugation or immersion). Depending on the nature of the electrochrome group, response times of the order of 100 ms may be obtained in display systems using these materials but their adhesion to the electrode is often limited.
Another process used for depositing thin polymer films on an electrode consists in electrochemically polymerizing the desired monomer. It is known to deposit, by anode oxidization, pyrrol and N substituted pyrrols on platinum or glass electrodes coated with a conducting oxide. In electrochemical display systems, these films may undergo oxidizing and reducing cycles with modification of the optical spectra. Although the electrodes coated with such polymers are advantageous because of the better adhesion of the thin electrochrom film, the materials have the drawback of being very sensitive to oxygen which promotes degradation thereof and reduces their life-span.
The invention, due both to Messrs F. GARNIER and G. TOURILLON of the Laboratoire de Photochimie Solaire of the C.N.R.S. and to Mlle GAZARD of THOMSON-CSF proposes palliating these disadvantages by providing an electrode coated with a polymer obtained by electrochemical polymerization of a monomer which belongs to a family allowing a product to be obtained with improved performances: reduced response time, great stability of the materials and improved life-span. In the case of using this electrode in an electrochemical display device, the color characterizing the display depends on the structure of the monomer and on the nature of the counter-ion.